Linearity dependence on oxygen fraction and gas temperature of a novel Fleisch pneumotachograph for neonatal ventilation at low flow rates

Abstract Fleisch pneumotachograph response is influenced by gas composition and temperature. Literature analysis shows that the influence of gas properties on the relationship between pressure drop and volumetric flow rate has not been widely investigated from the theoretical standpoint. We fit data reported in literature by multiple linear regression, with the aim to obtain an equation in which the dynamic viscosity of a gas mixture, mainly composed by nitrogen and oxygen, is directly related with gas temperature and oxygen fraction. A low dead space (2 mL) Fleisch pneumotachograph was designed and realized for neonatal ventilation, with linear range from −4 L min −1 to +4 L min −1 . The theoretical model, considering gas dynamic viscosity dependence on temperature and oxygen fraction, is presented and experimentally validated by varying gas temperature (299–310 K) and oxygen fraction (21–100%) within the limit conditions for the specific application. Oxygen fraction resulted the most influent factor on gas viscosity and, therefore, on the pneumotachograph response. In the worst case, the maximum variation of gas oxygen fraction produced a measurement shift of about 1 L min −1 , i.e., the 25% of full scale output. The introduction of a correction based on the proposed model allows to reduce the linearity shift, becoming lower than 6%, and may also reduce the need of frequent calibrations due to gas composition and temperature changes.

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